# std::numpunct

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Defined in header `<locale>` |  |
template< class CharT > class numpunct; |  |

The facet `std::numpunct` encapsulates numeric punctuation preferences. Stream I/O operations use `std::numpunct` through std::num_get and std::num_put for parsing numeric input and formatting numeric output.

The numbers that are supported by `std::numpunct` have the format described below. Here `digit` represents the radix set specified by the `fmtflags` argument value, `thousands-sep` and `decimal-point` are the results of thousands_sep() and decimal_point() functions respectively.

The format of integer values is as follows:

    integer     ::= [sign] units
    sign        ::= plusminus
    plusminus   ::= '+' | '-'
    units       ::= digits [thousands-sep units]
    digits      ::= digit [digits]

The number of digits between the `thousand-sep`s (maximum size of `digits`) is specified by the result of grouping().

The format of floating-point values is as follows:

    floatval    ::= [sign] units [decimal-point [digits]] [e [sign] digits] |
                    [sign]        decimal-point  digits   [e [sign] digits]
    e           ::= 'e' | 'E'

Inheritance diagram

### Specializations

The standard library is guaranteed to provide the following specializations (they are required to be implemented by any locale object):

Defined in header `<locale>`
std::numpunct<char> | provides equivalents of the "C" locale preferences
std::numpunct<wchar_t> | provides wide character equivalents of the "C" locale preferences

### Nested types

Type | Definition
`char_type` | `CharT`
`string_type` | std::basic_string<CharT>

### Data members

Member | Description
std::locale::id `id` [static] | the identifier of the facet

### Member functions

(constructor) | constructs a new `numpunct` facet (public member function)
(destructor) | destructs a `numpunct` facet (protected member function)
decimal_point | invokes `do_decimal_point` (public member function)
thousands_sep | invokes `do_thousands_sep` (public member function)
grouping | invokes `do_grouping` (public member function)
truenamefalsename | invokes `do_truename` or `do_falsename` (public member function)

### Protected member functions

do_decimal_point [virtual] | provides the character to use as decimal point (virtual protected member function)
do_thousands_sep [virtual] | provides the character to use as thousands separator (virtual protected member function)
do_grouping [virtual] | provides the numbers of digits between each pair of thousands separators (virtual protected member function)
do_truenamedo_falsename [virtual] | provides the string to use as the name of the boolean true and false (virtual protected member function)

### Example

The following example changes the string representations of true and false:

Run this code

    #include <iostream>
    #include <locale>

    struct french_bool : std::numpunct<char>
    {
        string_type do_truename() const override { return "vrai"; }
        string_type do_falsename() const override { return "faux"; }
    };

    int main()
    {
        std::cout << "default locale: "
                  << std::boolalpha << true << ", " << false << '\n';
        std::cout.imbue(std::locale(std::cout.getloc(), new french_bool));
        std::cout << "locale with modified numpunct: "
                  << std::boolalpha << true << ", " << false << '\n';
    }

Output:

    default locale: true, false
    locale with modified numpunct: vrai, faux

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 338 | C++98 | the `sign` token allowed an optional whitespace following `+` or `-` | removed the whitespace

### See also

numpunct_byname | creates a numpunct facet for the named locale (class template)

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